Electronic measuring instruments are used to collect information relating to the operation and performance of electrical and electronic circuits. Basic measuring instruments, such as ammeters and voltmeters, are used to measure currents and voltages of electrical signals in the circuit being analyzed (often referred to in the art as the “device under test” or “DUT”). These basic measuring instruments serve as building blocks for more complex electronic measuring instruments that are capable of measuring and providing information relating to the power, frequency, gain, attenuation, delay, etc. of test signals in the DUT.
Many types of electronic measuring instruments, for example, network analyzers, spectrum analyzers, and oscilloscopes, are designed to measure time-varying (e.g., alternating current (AC)) test signals. In general, these types of measuring instruments can provide accurate results only so long as the test signal being measured has a frequency within the permissible input frequency range of the measuring instrument. The permissible input frequency range of an electronic measuring instrument is, in general, determined and limited by the instrument's input frequency response. For most measuring instruments the input frequency response is flat only over a finite range of frequencies, typically ranging from a low measurement frequency limit close to zero hertz to an upper measurement frequency limit, beyond which the input frequency response begins to roll off.
To avoid errors and inaccuracies that can result from measuring test signals having frequencies beyond a measuring instrument's upper measurement frequency limit, a different (i.e., alternative) measuring instrument having a wider input frequency range must be used. Even when the frequency of the test signal is not higher than the upper measurement frequency limit, but is only near it, an alternative measuring instrument is usually used, since the dynamic range of a measuring instrument is usually best at lower frequencies.
Replacing a measuring instrument with an alternative measuring instrument is undesirable for a number of reasons. It is not only time-consuming, it can also be expensive, especially if the alternative measuring instrument is not readily available and must be purchased. The cost of acquiring an alternative measuring instrument can be particularly burdensome, given that measuring instruments with wider input frequency ranges tend to be more expensive than those having more restricted input frequency ranges. Replacing a measuring instrument with an alternative measuring instrument also undesirably shortens the useful lifespan of the measuring instrument being replaced, in some cases even rendering the measuring instrument being replaced obsolete.